1. Field of the Invention
The present invention relates to a feature of sharing copy data created by a storage system among a plurality of storage volumes provided in the storage system.
2. Description of the Related Art
Storage systems comprise features of generating an independently usable copy volume, without involving any host-computer software. A storage control device provided in such a system receives an instruction from external sources; and upon receiving this instruction, the storage control device carries out copying of, for example, a certain logical volume (a primary volume) within the storage control device, generates a copy volume, and forms a pair consisting of the primary volume and the copy volume. Then, by establishing a “split” state in which the synchronism between the primary and copy volumes forming the pair is broken and each of the volumes becomes accessible, for example, the process for resynchronization (a “re-sync” process) between the primary volume and the copy volume is stopped, and, on the other hand, the primary and copy volumes become available for separate uses, respectively. By separately using the respective primary and copy volumes that are in the split state, it becomes possible to conduct concurrent processing, such as carrying out batch operations and/or backup-obtaining operations in view of the copy volume while continuing an online operation with the primary volume. Accordingly, the availability of the storage system will be enhanced.
It is of course possible to use the above-mentioned copy volume as a backup volume for the primary volume. However, another problem arises when generating and operating a plurality of copy volumes that originate from one certain primary volume. That is, in case the primary volume and some of the copy volumes originating from that primary volume are used by different applications, there arises a need to further make a backup copy for each of the copy volumes, and it becomes inevitable to use “copies of the copy volumes” according to the number of copy volumes. Japanese Patent Application Laid-open Publication No. 2001-34426 discloses a system configured to comprise a plurality of copies of logical volumes.
In addition, unless the difference in data between the primary and copy volumes is managed for each pair upon updating the above-mentioned primary volume or each of the copy volumes, it will become necessary to copy the whole data in the volume, which is used as the source for backup, to the volume to where the data is to be restored. If it were to carry out such a restoring process for a plurality of copy volumes, an enormous amount of data will have to be handled during copying and other accompanying processes. Accordingly, there arises a possibility that the processing time will be extended, process efficiency will deteriorate, and the system load will increase. Anyhow, such a restoring process tends to lead to system complication and/or increase in operational loads.